The present invention relates generally to glass cutting and, more particularly, to the thermal cutting of relatively thick glass plates or sheets.
Various attempts have been made to thermally cut glass plates or sheets in an effort to overcome the arduous, time-consuming technique of scoring one surface of the sheet along a desired line of cut and then applying a bending force about the score line. This well-known procedure is especially tedious and costly when trimming the bulb edge of relatively thick glass sheets having thicknesses of 3/4 inch or greater because at least two, and sometimes three, successive trim cuts inwardly of such edge must be made in order to achieve a final satisfactory edge. Moreover, a finishing operation, such as belt seaming for example, is sometimes required for certain commercial applications.
Thermal glass cutting involves the application of heat to a surface of the glass along the intended line of cut to produce a thermal differential line through the thickness of the sheet and along which the compressive stresses adjacent the surface are decreased while the tensile stresses within the central region or core of the glass sheet are increased until reaching a level at which the glass will fracture along the thermal differential line. The most familiar of the various proposals for thermally severing glass involves the application of radiant heat along the intended line of cut from a non-contact thermal source spaced from the glass sheet surface. Also, one edge of the glass sheet is nicked to provide an edge score in alignment with the intended line of cut. As a practical matter, however, it has been found that the foregoing method of thermally severing glass is not always reliable in producing true linear cuts. It has been theorized that the reason for this resides in the fact that the radiated heat emanating from the source converges and enters the glass surface along the intended line of cut and then diverges as it migrates inwardly through the glass thickness. The progressively widening heated area creates at the tension layer, a heat band of substantially greater lateral extent than the thermal differential line. This can cause the glass to fracture uncontrollably in a meandering path along such band. Moreover, when attempting to make straight linear cuts parallel to the trim side of the blank where the desired line of cut is located inwardly of, or offset from, the centerline of the blank sheet, the cut has a tendency to run in an arcuate path toward the trim side to produce an arcuately curved or bowed edge projecting toward the trim side.